Interlocking circuits



April 14, 1936. f H CHA E 2,037,659

INTERLOCKING CIRCUITS Filed Dec. 15, 1935 www mvE N TOR OTTO H. SCHADE jrim- ATTORNEY Patented Apr. 14, 1936 UNITED STATES PATENT OFFICE INTERLOCKING CIRCUITS of Delaware Application December 15, 1933, Serial No. 702,451

6 Claims.

The present invention relates broadly to energizing circuits for amplifiers utilizing electronic tubes and more particularly to novel interlocking circuit arrangements for bias rectifiers.

Vacuum tube amplifiers require supply voltage sources for input (C-bias voltage) and output (B-voltage) circuits that are substantially independent of one another, at least within the amplified frequency range. Filter networks are commonly used to prevent A. C. reactions between B and C voltages if both are taken from a single supply source. In the case of very low frequency amplification these filter networks assume large proportions and finally cease to operate at zero frequency.

Class B operation of amplifier tubes at varying signal intensities, such as in broadcasting, causes considerable variation of the B supply current which in turn causes fluctuations of the B supply voltage. The magnitude of these fluctuations depends on the internal resistance of the B supply source. It is well known that variations of the C bias voltage of amplification has a considerably greater effect on the performance of the amplifier than variations of the B voltage. Obviously then, when the same source is utilized for the C and B voltage supply slight variations in the C bias voltage caused by variations of the B supply current produce undesirable effects. Superior results are, therefore, obtained with biased low frequency amplifiers, especially, those of the over-biased type (class AB or class B) if a separate voltage supply system for bias voltages is provided. In accordance with the present invention the bias voltage is conveniently supplied from a separate rectifier circuit. The power required is usually small so that a vacuum tube rectifier of relatively low saturation current may be used successfully for this purpose.

In a particular practical embodiment of the invention it was found that utilizing one diode contained in a type 55 amplifier tube gave com mendable results. If a separate rectifier tube or diode is used to furnish bias voltage to other amplifier tubes it is necessary to provide means for interlocking the bias rectifier and the other amplifier tubes in such a way that removal of the rectifier tube and thus taking off the bias voltages, does not cause destruction of the tubes normally receiving bias voltage from this rectifier.

Objects of the invention are to provide simple but effective interlocks between the biased tubes and the biased rectification circuits so that the power tubes may be protected should' the bias rectifier burn out or be removed as when replaced. Still other objects of the invention are to improved generally the simplicity and efficiency of energizing circuits for vacuum tubes and particularly to provide an economical and compact form of bias rectifiers and interlocking arrangements for amplifier circuits and the like which is not only reliable in operation but may be economically manufactured and assembled. The novel features which are believed to be characteristic of the invention are set forth in particularity in the appended claims.

The invention itself, however, both as to its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which there is indicated diagrammatic-ally several circuit arrangements whereby the invention may be carried into effect.

In the drawing, Figure 1 illustrates a double rectifier arrangement for plate voltage and bias voltage supply wherein both supplies are interlocked;

Figure 2 illustrates the invention as applied to a pair of power tubes in push-pull containing diodes which are used for C bias purposes, the bias voltage interlock being provided in the power tubes themselves;

Figure 3 illustrates another modification of the broad principle illustrated by Figure 2 and providing better results; and,

Figure 4 illustrates a modification of the invention wherein a separate bias rectifier of the full wave type is used and wherein the tubes to be biased become self-biased if the separate bias rectifier is removed at which time the filament circuit of the power tubes is opened.

Broadly construed the present invention provides three methods of protective interlocks. The first of these methods which is illustrated generally by Figure 1 provides a bias rectifier and plate voltage rectifier enclosed within a single envelope. The cathodes of both of these rectifiers are heated by the same current. In other words, the heating circuits are in series. The interlock is provided by reason of the fact that one of the rectifiers cannot be removed without the other since they are both within a single enclosure; also a burn-out of the heater will affect both rectifiers simultaneously, since, as previously stated, the heating circuits are in series and the same current traverses both thereof.

The second method utilizes a bias rectifier (diode) which is contained in the envelope of the tube receiving the bias voltage. Both Figures 2 and 3 illustrate this method. It is quite obvious from a consideration of the drawing that the bias rectifier cannot be removed without removing the tube and further that a heater burnout affects both the bias rectifier and the tube receiving the bias voltage since they both have the same cathode.

The third method incorporates a separate bias rectifier tube and is illustrated generally by Figure 4. The interlock in this case is provided by means of a socket contact opening the filament circuit of the biased tubes and removing a shortcircuit across a self-bias resistor. The socket contacts are made by one of the heater pins of the bias rectifier in connection with two auxiliary pins thereof. On removal of the bias rectifier tube a self-bias resistor is, so to speak, thrown in and the drop across this resistor provides a bias voltage for the tubes. At the same time the filament circuit of these tubes is opened so that the cathodes thereof become cold or at least have a lower temperature when the bias rectifier is re-installed in the socket. In this arrangement as the bias rectifier does not provide a bias voltage until its cathode starts to emit the amplifier tubes may draw relatively heavy plate currents if the biased rectifier is quickly replaced by a cold tube (the self-bias resistor is shorted when the bias rectifier is inserted), hence, the bias rectifier tube should have a short heating time so as to shorten the time of overload current on the amplifier tubes to a minimum.

However, it has been found in practice that an exchange of the bias rectifier tube requires sufficient time to lower the emission of the amplifier tubes sufiiciently to prevent severe overload currents.

While the energy for the bias voltage rectifier has been shown as derived from the commercial power supply mains or power transformer it should be understood that any suitable source may be utilized for this energy, as for instance, the local oscillator in superheterodyne receivers.

In Figure 1 the power transformer PT is provided with primary winding 3 and two secondary windings 4 and 5. The primary winding 3 is adapted to be connected across commercially available alternating current power mains through the medium of terminals I and 2. A tube T1 is provided having within a single envelope tworectifiers; one a full wave rectifier and comprising two plates I1 and I8 and a single indirectly heated cathode I4, and the other a half wave rectifier comprising a single plate I6 and an indirectly heated cathode I5. The heating circuits for the two cathodes I4 and I5 comprise heaters I2 and I3 which are connected in series across the secondary'4. Thus, the same current traverses both heaters I2 and I3. The midpoint of the secondary 4 is grounded as at G. Conductors 8 and 9 connected to the secondary are provided for the heater circuits of other tubes, as for instance, the amplifier tubes of a radio receiver. The anodesI'I and I8 of the full wave rectifier are connected respectively to the opposite ends of the secondary 5. The latter has its midpoint 6 grounded as at G. Cathode I4 is connected through a suitable choke I9 to a terminal 23 which may be considered the plus B terminal of the rectifier filter arrangement. A suitable filter condenser 28 is shunted between ground and. one end of the choke coil. It is obvious that choke I9 and condenser 20 form a filter unit for filtering the B supply. It is to be understood, of course, that the B supply is fed through suitable means as voltage reducing resistors to the portions of the amplifier requiring plus voltages. The cathode I5 on the other hand, is connected to a point I on the secondary 5, while the anode I6 is connected to a terminal 24 which may be considered the negative terminal of the arrangement. To this terminal 24 are connected the elements of amplifier tubes requiring a bias voltage.

A filter condenser 2| is provided between the anode I6, terminal 24 connection and ground and a'regulatory resistor 22 is shunted across the condenser 2 I.

It is obvious from the above description and from the drawing that the half wave rectifier is, so to speak, inverted with respect to the full wave rectifier so that as regards D. C. voltages the cathode I5 is at the same potential as the anodes I? and I8. The portion of the secondary between points 6 and I is usedfor deriving the A. C. for the half wave rectifier.

The interlock in the caseof the system shown in Figure 1 isprovided by reason of the fact that the bias rectifier which is shown .as the half wave rectifier cannot be removed without removing the B supplyrectifier or the full wave rectifier. Also, in view of the fact that the heater circuits are connected in series a burn-out in one will necessarily disable the other as previously disclosed.

While the tube T]. has been shown .as comprising a full wave rectifier and a half wave rec- -tifier, it is to be distinctly understood that the tube may comprise two full wave rectifiersor two half wave rectifiers and that the arrangements of B supply and C supply may be reversed, that is to say, the B supply may be derived from a half wave rectifier whereas the C bias supply may be derived from the full wave rectifier.

In Figure 2 the power transformer'PT is provided with a primary 3 and two secondaries 25 and 26. Primary 3 is adapted to be connected to the mains of commercially available alternating current by means of the terminals -I and 2. A full wave rectifier T2 is provided with a cathode connected across the secondary 25 and two anodes connected respectively to opposite ends of the secondary 26. The midpoint 21 of secondary 26 is grounded as at G. A push-pull amplifier including'a pair of electronic tubes T3 and T4 of any type of amplifier circuit is shown energized by the full wave rectifier T2. Tube T3 is provided with the usual anode, cathode and control electrode and in addition a. diode plate 45. Tube T4 is similarly constructed in that it is provided with an anode, cathode and control electrode and a diode plate 46.

The anodes of tubes T3 and T4 are respectively connected to opposite ends of the primary of ;an output transformer 42, the secondary of which is connected to a suitable translating device or the like. The cathode point of the rectifier T2 is connected through a suitable filter choke 32 to the midpoint of the primary winding of transformer 42. This connection is provided so that the anodes of tubes T3 and T4 may be supplied with the necessary energizing potential. Filtering of this potential is performed by the circuit comprising choke 32 and grounded condensers .30 and 3| in customary fashion. The input to the tubes T3 and T4 is provided by means of an input transformer comprising primary'winding 35 and secondarywinding 36, the energy to be amplified be applied across terminals 33 and-34 of primary winding 35, the opposite ends of the secondary 36 being connected respectively to the control grids of tubes T3 and T; as shown. A common portion of input circuit of both tubesTa and T4 connects both cathodes 43 and 44 to the midpoint of secondary 36 through a pair of resistors 31 and 38.

Diode 45 is connected directly to diode 46 and a common connection from both diodes is provided through a condenser 29 to a point 28 of the secondary 26. The cathode end of the resistor 38 is grounded as the G while a suitable condenser 39 is connected between the secondary end of the resistor 31 and ground.

From the above it can be seen that an alternating current as derived across portion 21, 28 of secondary 26 is impressed across the resistor 38 and that this alternating current is rectified in one instance by the action between diode 45 and cathode 43 and in anotherinstance between the action of diode plate 46 and cathode 44. It is also evident that the resistor 38 is in the grid circuits of both tubes T3 and T4, hence, the drop across the resistor 38 caused by the flow of unidirectional current therein is utilized to bias the control grids of the two push-pull tubes. Resistor 31 and condenser 39 are provided so as to form a filter circuit which acts to attenuate the ripple voltage, hence, producing a smooth bias voltage for the two push-pull tubes.

The necessary heating current for the heating circuits of cathodes 43 and 44 is connected to terminals 40 and 4| in any suitable manner.

As previously inferred the interlock in the case of Figure 2 is provided by reason of the fact that the bias rectifier being within the same envelope as the amplifier tube cannot be removed without removing the amplifier tube itself. Also, heater burn-outs affect both simultaneously. Whereas, the invention in Figure 2 has been described in connection with a pair of tubes in push-pull it is obvious that any other type of amplifier circuit may be employed as, for instance, a single amplifier tube.

Figure 3 is somewhat similar to the arrangement shown in Figure 2 except that the bias voltage is derived across a resistor 58. For this purpose the power amplifier PT is provided with an additional secondary winding 52; one end of which is connected to the center point of the sec.- ondary 36 of the input transformer, while the other end is connected to both diodes 45 and 46 of tubes T3 and T4 respectively. The common cathode connection of the two tubes is shown grounded as at G. A connection is provided from the first mentioned end of secondary 52 to ground, this connection including a bias resistor 50 shunted by a by-pass condenser 49. From a study of Figure 3 it will be seen that the alternating current derived across the secondary 52 is rectified by the diode rectifiers 45, 43 and 46, 44 thereby causing the rectified current to pass through the resistor 50. This resistor is connected in the grid circuits of both tubes T3 and T4, hence, supplying the necessary bias voltage. Condenser 49 is utilized so as to by-pass the applied A. C. voltage so as not to develop a large ripple voltage component across the resistor 58.

In the system shown in Figure 3 the interlock is provided in the same manner as described in connection with Figure 2 and it is to be understood that the system shown in Figure 3 may be applied equally well to a single tube amplifier arrangement in place of the push-pull circuit shown.

In Figure 4 a biasing rectifier tube T7 is provided having four pins 62, 63, 64 and 65. The pins 62 and 63 are utilized to feed energy to the heating element 6|. Cooperating with the heating element Bl are two cylindrical cathodes 51 and 58, these being connected to points 58 and 54 respectively of the secondary 26. The midpoint 55 of the secondary 26 is grounded as at G. Tube T7 is also provided with a pair of anodes 59 and B8. Anode 59 cooperates with the cathode 58, whereas, anode 68 cooperates with the cathode 51. The two anodes are connected together and by a common conductor 13 are connected to midpoint of the secondary 36 of input transformer. The bias for the tubes T and T6 is provided by reason of the fact that the drop across the bias resistor 12 is impressed upon the grid circuits of the tubes T5 and T6. The rectifier tube T'z may be considered as a full waverectifier in inverse relation to the rectifier T2 so that the potentials developed by the rectifier T1 are negative and may be utilized for biasing purposes. Condenser H is. provided to by-pass the applied A. C. voltage so that it does not develop a large ripple voltage across resistor 12. The proportion between terminals 56 and 54 of secondary 26 is utilized for feeding the A. C. to the cathodes 57 and 58 of rectifier T7. The secondary 53 is utilized to furnish current to the heater of tubes T5 and T6 as well as to the heater element BI and is additionally provided with terminals 66 and 61 for feeding energizing currents to any other heaters of the system. A self-bias resistor 15 is connected across the connections 69 and from pin terminals 64 and 65 respectively so that upon removal of the tube T7 from its socket the resistor comes into play as a self-bias for the tubes T5 and T6 and thus prevent damage to the tubes while the cathodes thereof remain hot. It should be noted that removal of the tube T? from its socket not only breaks the circuit at points 62 and 63 and also breaks the circuit at points 64 and 65 so that the short-circuit across resistor 15 is removed. When the tube T7 is again replaced in its socket a short-circuit is provided across the resistor 15, thus preventing its affecting tubes T5 and T6.

The interlock in the circuit arrangement described in Figure 4 is provided by reason of the fact that the removal of tube T1 breaks the filament circuit of the amplifier tubes T5 and T6 and further conditions resistor 15 so as to act as a self-bias to protect the tubes T5 and T6 while the cathodes thereof remain hot.

While there has been indicated and described certain specific arrangements for carrying the invention into effect it will be apparent to anyone skilled in the art that the invention is by no means limited to the particular organizations shown and described but that many modifications may be made without departing from the scope of the invention as set forth in the appended claims.

I claim:-

1. In a power supply system for electronic tubes, a double rectifier for plate voltages and bias voltages comprising a full wave rectifier of the electronic type and a half wave rectifier of the electronic type, an indirectly heated cathode for said full wave rectifier, an indirectly heated cathode for the half wave rectifier, and a single heating circuit for obth cathodes.

2. In a power supply system adapted to energize electronic tubes and the like said system being arranged so as to supply separately plate current for the tubes and biasing potentials therefor, a first rectifier unit comprising an anode and a cathode, a power transformer provided with means for connecting the primary thereof to a source of alternating current energy, a first load and means for connecting the first rectifier unit, said load and the secondary of the transformer in series, a second rectifier unit comprising an anode and a cathode, a second load and means for connecting the second rectifier unit, the second load and at least a portion of .the secondary of said transformer in series, a single heating circuit for both said cathodes, said two rectifiers being connected inversely with respect to .each other and the secondary winding of the transformer.

3. In a power supply system arranged for energizing electronic tubes of the type requiring anode potentials and biasing potentials, a first rectifier unit comprisingan anode and a cathode,

a power transformer provided with means for connecting the primary thereof to a source of .alternating current energy, means for connecting the first rectifier unit to the anode of the electronic tube to thereby supply theele'ctronic-tube with anode potential, a second rectifier unit comprising an anodeand a cathode, means forconnecting said second unit to the grid electrode of the electronic tube to thereby supply said tube with a biasing potential, means for establishing a direct current connection between the cathode of the second rectifier unit and the anode of the first rectifier unit whereby the cathode of the second unit is maintained at substantially the same direct current potential as the anode of the first unit and a single heating circuit for the cathodes of both said rectifier units.

4. In a power supply system, a double rectifier for plate voltages and bias voltages comprising, a pair of anodes and an indirectlyheated cathode disposed with respect to each otherso as to form a full wave rectifier, an indirectly heated cathode and an anode disposed so as to form a half wave rectifier, a power transformer including a pri- -{nary provided with means for connection to an available source of alternating current and a secondary, a connection from one of saidfirst two named anQ es to one end of said secondary and a connection from the other of said first two named anodes to the other end of said secondary, a first terminal and a connection from the first named cathode to said first terminal, said connection including a reactor device, a connection between a second named cathode and a pointinterrnediate the .two ends of the secondary, a second terminal and a connection between the anode of the halfwaverectifier and said second terminal, a common heating circuit for both said cathodes and means for connecting the cormnon heating circuit to the source of alternating current.

5. In an energizing circuit for an electronic tube of the type having at least an anode, a cathodeand a grid electrode, a source of alternating current, a rectifier circuit coupled to said source and adapted to rectify energy from the source, a filter circuit connected to the rectifier output for smoothing out the rectified current and means for impressing the smoothed rectifier output across the anode and cathode of said tube to thereby maintain the anode at a positive .potential with respect to the cathode, a second rectifier circuit coupled to the source of alternating current and arranged in inverse sense with respect to the other rectifier circuit whereby the second named rectifier output is of negative potential with respect to the output of the first rectifier; a connection between a grid electrode of the electronic tube and a point of the output circuit of the second named rectifier having a potential which is negative with respect to the cathode of the electronic tube whereby said grid electrode is vbiased with respect to the cathode of the tube and means for interlocking said two rectifier circuits so as to prevent operation of eitherthereof when the other is rendered inoperative.

6. A system as describedin the next preceding claim wherein each of said rectifier circuits includes a thermionic rectifier, each rectifier being provided with at least one anode and a cathode, and wherein the interlocking means for the two rectifier circuits comprises a single energizing circuit for both cathodes.

OTTO I-I. SCI-IADE. 

